This is a proposal to determine the composition of genomes and characterize two moderately repeated genomic constituents, rDNA and a transposable element, of three tick species, Ixodes dammini, Dermacenter variablis, and Amblyoma americanum, all of which are putative vectors of lyme disease. These initial studies would facilitate future studies of vector systematics (including identification of cryptic species), ecology (e.g., population structure), developmental biology, and genetic control. In addition, a preliminary systematic analysis of 18 tick genera would be conducted using two DNA sequences, a semi-conserved sequence of the 28S rRNA gene and part of the reverse transcriptase gene of a retrovirus- like transposable element. The percentage of each genome composed of highly repeated, moderately repeated, and single copy DNA would be determined by reassociation kinetics. Genomic libraries would then be constructed in order to clone and subclone moderately and highly repeated DNA. Genomic libraries would be probed with whole genomic DNA to reveal clones that are repeated (the degree of repetition correlating with intensity of autoradiographic exposure). Libraries will also be probed with PCR-amplified conserved sequences of rDNA to obtain complete rDNA repeating units and with degenerate PCR amplifications of reverse transcriptase sequences of retrovirus-like elements to obtain transposable elements. Variation among genera in the copy number of characterized sequences/elements would be estimated by quantitative laser densitometry. Some rDNA units and transposable elements would be sequenced while others would be mapped with restriction enzymes to reveal sequence diversity within multigene families. Thus, short (500 bp) sequences will be identified for use in the proposed systematic analysis while other sequences will be revealed for use in future systematic studies at higher and lower taxonomic levels.